It is not a problem of brick, it is a problem of Traits in pharo.
In brick we have a few traits that use��GLMBrickExtensionTrait, for example:
Trait named: #GLMBrickLayoutTrait
�� uses: GLMBrickExtensionTrait
�� category: 'Glamour-Morphic-Brick-Traits'
self traitComposition allTraits returns collection of 7 traits including��GLMBrickExtensionTrait. But implementation of��transformationOfTrait: refers to��transformations which is an array of 4 traits directly used by GLMBrick, so obviously��GLMBrickExtensionTrait is not found -> nil.
So��flattenDownAllTraits is broken and does not take care about "subclassing" of bricks.